The NIH is one of fourteen centers in this prospective, multi-center, double-blind, randomized, placebo-controlled study. The objective is to determine the safety and efficacy of nitric oxide for inhalation in the treatment of vaso-occlusive pain crisis in patients with sickle cell disease and to validate an approved device for transcutaneous measurement of methemoglobin in a population of patients with sickle cell anemia.. The study population will include patients with sickle cell disease (SS, S-beta-Thalassemia) presenting with vaso-occlusive pain crisis. Patients will be 10 years of age or above and will be administred either placebo or inhaled nitric oxide to see if the experimental agent, inhaled nitric oxide, can reduce the time it takes for resolution of the vaso-occlusive crisis. We began pre-enrolling in January 2005 and to date have pre-enrolled 125 subjects. Of these 125 subjects, 49 have actually enrolled and been randomized to either placebo or nitirc oxide and an additional 13 more subjects who were not pre-enrolled have also been randomized in the study bringing the total number of subjects at the NIH randomized to the study to 62. Of these 62 subjects, 5 have been children. The other participating sites have also begun enrollment. This brings the number of subjects randomized in the treatment study to 139. There are only 11 more subjects needed to complete enrollment for this multi-center study.[unreadable] [unreadable] Due to the double-blind nature and the design of this trial, no preliminary data analysis will be available until completion of the entire study.[unreadable] [unreadable] This protocol has been reviewed by the Pulmonary DSMB of the NHLBI 8 times and has consistently been recommended for continuation. The DSMB has reviewed the unblinded Serious Adverse Events and the methemoglobin values of all subjects enrolled as of March 2008 and no safety concerns were appreciated at that time.